I agree with Karateblossom.
..if your garage is set up correctly, dog proofed and climate controlled (insulated garage) then if that's where the dog will sleep, let him sleep there. I agree that you have to commit to this and maybe he will never be an inside sleeper, but if you are okay with that for the long run, then okay.
I posted a couple of weeks ago about Kana not wanting to come inside at night. We all went back and forth about the reasons why (too hot inside, needs space)and the BPO'ers had
great advice, but in the end you have to be comfortable to make your own decisions that fit your life and your dog. If the dog is safe and quiet...what's the problem?
The dog door is a great solution to the problem if it's feasable. Tha's what we did.
By the way, Kana's outdoor sleeping phase has come to an end. He is back in the house at night, sleeping next to mom where she wants him
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Please keep us updated about the progress!!! Hopefully you will have a resolution soon so that you can sleep soundly at night!!!!!